Some models of the Yamaha R1 have an intentional flat spot in their fuel maps which happens to be right at the spot where testing happens, too.
In a similar vein, the Aprilia RSV4 kind of cheats at noise testing: in neutral, there is a baffle which flips down to dampen the exhaust note a bit. :)
Almost all supersport bikes coming into the US utilize both of these strategies. :)
I own a Ducati 999 that was lemonlawed because it would stall at stop lights. Super common and happened because of how lean the bikes had to run to pass US emissions.
Google said "random stalls" were kind of endemic to Ducatis. :P Didn't know it was related to the fuel mapping! I had a 1098 which would occasionally (maybe once per month) randomly stall at 0% throttle when braking to a stop. I had a full Termignoni system + race ECU, though. California doesn't do emissions testing on bikes, surprisingly!
I had to put a Power Commander on my R1 because of the aforementioned lean spot. The engine would "chug" at about 37mph (5.2k rpm in 1st gear), which unfortunately happened to be a very common cruising speed. Google showed lots of complaints for other years as well.
In a similar vein, the Aprilia RSV4 kind of cheats at noise testing: in neutral, there is a baffle which flips down to dampen the exhaust note a bit. :)